Most conditions describe the present: price is above the average, RSI is low. But a lot of good ideas are about events and history. The moment a line was crossed. How many bars since the last breakout. The high of the bar that broke out. The second push, not the first.
The Crossover turns "crosses above" into one event that's true on exactly one bar. Since and Capture give a strategy memory: Since counts bars since a condition last held and how often it happened, and Capture remembers a value from the bar it held. The State Machine goes furthest, holding a pattern with stages and counts. Event Day knows the scheduled market events, like FOMC days, CPI releases and options expiry.
Crossover
The bar where one value crosses another, and bars since it happened.
Since
Bars since a condition last held, and how often it happened.
Capture
The value of something at the bar a condition held.
State Machine
A pattern with memory: stages, the moves between them, and counts.
Event Day
FOMC, CPI, NFP, options expiry and roll days.